Climatic variability in Ziro lake Basin

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Late Quaternary climate variability and vegetation response in ZiroLake Basin, Eastern Himalaya: A multiproxy approach

Ruby Ghosh a, Dipak Kumar Paruya b, Mahasin Ali Khan b, Supriyo Chakraborty a,c,Anindya Sarkar d, Subir Bera b,*

aBirbal Sahni Institute of Palaeobotany, 53, University Road, Lucknow 226007, IndiabCentre of Advanced Study, Palaeobotany-Palynology Laboratory, Department of Botany, University of Calcutta, 35, Ballygunge Circular Road,Kolkata 700019, Indiac Indian Institute of Tropical Meteorology, PunedDepartment of Geology & Geophysics, Indian Institute of Technology, IIT Kharagpur, Kharagpur 721302, India

a r t i c l e i n f o

Article history:Available online 26 February 2014

a b s t r a c t

Pollen, phytolith and stable carbon isotopic records provide new insights into the palaeoenvironmentaland palaeoclimatic changes in Ziro Lake Basin, sub-Himalayan Arunachal Pradesh, India since pre-LGMtime. Phytoliths record a minor change in grass/woodland cover and appear to be more sensitive thanpollen grains to climate fluctuations. Both pollen and non-pollen palynomorph data suggest prevalenceof a dense C3 species-dominated moist semi-evergreen forest in the area until the LGM which showsconformity with d13C data. The phytolith assemblage indicates an alteration in forest cover withexpansion of C4 grasses during the LGM. The study further indicates a climatic amelioration withintensification of south-west monsoon during 10.2e3.8 ka and an expansion of forest cover. After 3.8 kathere was a rising trend of dryness, shrinkage in forest cover, and a slight increase in C4 species while C3plants dominated. Ecosystem variability also points towards a hydrological transformation in the areasince pre-LGM time. Application of coexistence approach on pollen data reveals that prior to the LGM themean annual temperature and mean annual precipitation were approximately 19.3 � 0.001 �C and1925 � 15 mm respectively. Between 10.2 and 3.8 ka MAT was about 19.4 � 0.5 �C, while MAP was1901 � 41.3 mm. Between 3.8 and 1.2 ka and onwards a slight increase in MAT (w0.3C�) was observedwith further decrease in MAP to 1861 � 33.4 mm. During pre and post LGM times, MAT was more or lesssimilar in the Ziro Lake Basin which increased gradually after 3.8 ka and was w1.2 C� higher than today.Prior to the LGM, MAP was higher than the present day by 94 mm, between 10.2 and 3.8 ka by 70 mmand since 3.8 ka onwards by w30 mm showing a tendency of gradual decline suggesting a consequentincrease in dryness.

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1. Introduction

The Himalayas influence the meteorological conditions of theIndian subcontinent, Central Asian highlands and Southeast Asia byacting as a climatic divider and helping in circulating the air andwater systems to a great extent. They also play a significant role inmonsoon dynamics (Prell and Kutzbach, 1992; Yang, 1996; Guptaand Anderson, 2005; Bhattacharyya et al., 2006). The uplift of theHimalayas during the Neogene (varying from a few up to 2000 andmore metres) had resulted into disruption in channel and

formation of a number of intermontane lakes (Iwata, 1987; Selby,1988; Meetei et al., 2007; Srivastava et al., 2009b and referencestherein). Interplay of climate and tectonics may be accredited tothis geomorphic development of the Himalayan mountain chain.Some studies on the Quaternary valley fill deposits (Meetei et al.,2007) and deposits from lake basins have linked tectonic activitywith climatic variability behind their evolution (Burbank andJohnson, 1982; Burbank, 1983; Bhattacharyya, 1989; Kotlia et al.,1997; Shukla et al., 2002; Dill et al., 2003; Juyal et al., 2004;Srivastava and Misra, 2008; Srivastava et al., 2009a,b). Hence, theQuaternary deposits from the mountain valleys and intermontanelake basins may serve as archives for studying the changes in formof valleys/basins and stratigraphic architecture induced by pertur-bations in the tectonic climate system. It is known that climate

* Corresponding author.E-mail address: [email protected] (S. Bera).

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influences plant growth and vegetation types of any region andplant records are known to be direct proxies that can be used toreconstruct the climatic factors quantitatively. The formation andsuccession of the natural forest, the vertical and horizontalexpansion of the forest zone are known to be controlled by climaticfactors including temperature, precipitation, humidity and manyothers. Forest vegetation is sensitive to even a mild alteration intemperatureeprecipitation regime. So, it is needed to identify theprincipal climatic drivers influencing the vegetation dynamicscoupled with geomorphic evolution of this region through ages.Eastern part of the Himalayas significantly differs from of itswestern and central parts due to its more humid climate andgreater biological diversity. The marked climatic differences acrossits northesouth gradient owing to the complex steep topography ofthe vast reach of mountains and its location at the juncture of twocontinental plates (Asian and Indian plates) attribute exceptionalclimatic as well as biological diversity to this region.

Most of the earlier studies from the Eastern Himalayas on theQuaternary deposits from intermontane lake basins and valley filldeposits have focused on geomorphic studies, palaeoseismicstudies, and chronology developments (Meetei et al., 2007;Srivastava and Misra, 2008, 2012; Srivastava et al., 2009a,b).However, the response of the plant communities to these coupledgeomorphic and climatic changes was not attempted earlier fromthe above-mentioned valleys or intermontane basins. Some ac-counts on the Quaternary climatic history from this region (Sharmaand Chauhan, 1994, 1999; Chauhan and Sharma, 1996; De et al.,2001; Sharma and Chauhan, 2001; Bhattacharyya et al., 2007;Shah et al., 2009) focused on the variability of past climate,although not considering tectonicseclimate interactions. Further, ifwe consider the key role of the Himalayas on the Indian monsoondynamics (Sanyal, 2007), the scarcity of data from the eastern partis disconcerting, in particular when tectonic movements andclimate oscillations are coupled. Only further study can verify howthe plants showed sensitivity to climate change in the EasternHimalayas with corresponding tectonic events and help to shedlight on whether these signatures of climatic variability are local orregional.

The geomorphic evolution of ‘Ziro’e an intermontane lake basinin sub-tropical belt of the Arunachal Himalaya was earlier studiedby Srivastava et al. (2009b). Present study aims to identify the cli-matic variables influencing the distribution of the plant commu-nities during the late Quaternary tectonic upliftment in this part ofthe Himalayas and further to gain information on past environ-mental changes and corresponding response of plant communitiesusing pollen, phytolith, and stable carbon isotope proxies. All ofthese proxies provide qualitative palaeoclimate information,although there has been a sustained need to quantify past climatechanges from proxy records to better understand the drivingmechanisms and to improve future climatic predictions. However,due to limited knowledge of the proxies and the climate mecha-nism, sometimes the quantitative results remain inconclusive(Ning, 2010). The most widely used method of quantitative palae-oclimate estimation, the transfer functions, are still random withrespect to implementation of the process. Sometimes the bestregression model based on the F-test lacks sufficient scientific ev-idence (Zhang, 1988). Therefore, for quantitative reconstruction ofthe climate, the reliability and effectiveness of the proxy and themethod are vital.

Considering the climatic sensitivity of plants, the coexistenceapproach (CA) (Mosbrugger and Utescher, 1997), is applied here forquantitative reconstruction of the palaeoclimate of the region. Themost significant prerequisite of this analysis is that the climatictolerance of the fossil plants should be similar to their nearest livingrelative taxa. As the Quaternary plants have evolved after a long

term natural evolution, their ecological and climatic tolerances aresimilar to modern plants. Hence, the CA may be used here effec-tively for obtaining quantitative information on climate and toreconstruct the climatic factors quantitatively with the aim ofdiscovering the nature of climatic oscillations coupled withgeomorphic evolution of the basin and resultant vegetationresponse in this part of the Eastern Himalayas since pre-LGM time.

2. Study area

Quaternary deposits are represented by fluvial, glacial andfluvio-lacustrine sediments in the Arunachal Himalayas. Lake Zirois a NeS trending lake situated at an altitude ofw1600m a.s.l in theLesser Himalayan ranges. This part of the Lesser Himalayan regionof Arunachal Pradesh is neo-tectonically evolved and the tectonicactivity is dated to be 22e14 ka by OSL (Srivastava et al., 2009b).Study of the lakebed profile by Srivastava et al. (2009b) suggests anNeS asymmetry in the basin geometry and further indicates thatthe southern part of the basin is geomorphologically rejuvenated.In the northern extremity (first w6 km) the lakebed gradient isw4.5 m/km, and the relict sedimentary deposits are preserved as a<10 m high mound within the basin. In the southern part thegradient rises to w10 m/km, and 20e25 m thick sequences arefound exposed on the lakebed. Kale River, a low gradient tributaryof the Subansiri River, drains the valley and thick organic richblackish silt dominates the modern lakebed (Fig. 1). This sequencewas formed due to activity of fluvial agencies resulting from theretreat of the glaciers followed by deposition of lacustrine sedi-ments including clay, carbonaceous clay, and peat. The vegetationof this area is categorized as mixed sub-tropical broad-leaved andpine forest (Hajra et al., 1996; Dollo et al., 2009) represented bythree species of Pinus viz., Pinus merkusii, Pinus roxburghii and Pinuswallichiana along with Alnus, Betula, Lyonia, Quercus, Tsuga, andRhus, and others. The non-arboreals are primarily represented byAjuga, Coriaria, Desmodium, Elsholtzia, Indigofera, Luculia, Plec-tranthus, Pogostemon, Potentilla, Pteridium and Rubus (Hajra et al.,1996). The mean annual precipitation of the area is w1831 mmand mean annual temperature is w18.5 �C [http://www.cru.uea.ac.uk/data 3.1, 0.5� � 0.5� gridded versions, 1901e2009; (Mitchell andJones, 2005)] (Fig. 2).

3. Materials and methods

Samples for the present analyses (pollen, phytolith, and d13C)were collected from a 3.4 m long profile exposed along Soro nala (aKale river tributary) (93� 490 49.2400 N; 27� 320 01.2200 E; altitudew1557 m a.s.l), of Ziro Lake Basin (Fig. 1). Lithologically, the top150 cm of the profile is composed of blackish carbonaceous clayeysilt followed by a 150 cm sequence of coarse sand and conglom-erate, overlying a zone of 40 cm thick grayish layers of alternatingsand and silt (Fig. 3). Samples collected at each depth were dividedinto three parts and kept separately for pollen, phytolith, and d13Canalyses. Samples for radiocarbon dating were selected from clayeysilt layers, kept separately in aluminum foil, and sealed in plasticbags to avoid contamination.

The samples collected from coarse sand-conglomerate sequencehave been excluded during stable carbon isotopic analysis. Asorganic matter (and d13C compositions) within sands may not al-ways reveal the in situ origin, it will not reflect true isotopicsignature, and hence was not included during isotopic analysis.

A total of eighteen samples have been analysed from the wholeprofile for carbon isotopic (d13C) compositions of bulk organicmatter (samples from layer of conglomerate and coarse sands havebeen excluded). About 50mg of each powdered dried decarbonatedsediment sample was combusted in a Flash elemental analyzer in

R. Ghosh et al. / Quaternary International 325 (2014) 13e2914


an oxygenated environment. The evolved CO2, purified through amoisture trap, wasmeasured for its isotopic compositions in a DeltaPlus XP continuous flowmass spectrometer at IIT, Kharagpur, India.Typical experimental precision was w�0.1&. All isotopic data arereported against PDB.

Chronology of the profile was established by using two 14Cradiocarbon dates of two organic rich clayey silt samples dated atRadiocarbon Dating Laboratory of Birbal Sahni Institute of Palae-obotany, Lucknow, India and two IRSL dates (on coarse grainedfeldspar) obtained from two neighbouring sections of Ziro LakeBasin, previously published by Srivastava et al. (2009a,b) for betterinterpretation of palaeoclimatic events (Table 1). The radiocarbondates were calibrated to calendar dates before present (BP) usingthe radiocarbon calibration program Calib 6.1 of Reimer et al.(2009) and reported as ka. Table 1 also provides information onthe GPS locations of the profiles, length of the profiles, materialsdated, and ages obtained.

Extraction of palynomorphs from the sediments was donefollowing the standard palynological technique including drying,weighing, HCl (10%) treatment for carbonate removal, overnight HF(40%) treatment, heavy liquid separation (KI þ CdI2; sp. gr. 2.3) andacetolysis (Erdtman, 1954). Slides were prepared using polyvinylalcohol. Threeefour slides were prepared for each sample, anaverage of 300 palynomorphs were counted, observed and photo-graphed under a Zeiss Axioskop 2 compound light microscope atca. �400 magnification.

Phytoliths were extracted following the procedures of Kelly(1990), Fredlund and Tieszen (1994) and Pearsall (2000) withminor modifications. In each case, a minimum of 20 g of sedimentsample was taken, dried using hot air oven at 60 �C, crushed andsieved through 10 mm sieve. Organic matter oxidation was doneusing H2O2 and densi-metric separation using CdI2 þ KI (sp. gr.2.3). The extracted phytoliths were mounted on slides usingCanada balsam. More than 400 phytoliths were counted in eachcase (besides poorly yielded samples from sand-conglomeratedeposit) under the above-mentioned microscope at �400magnifications.

For the extraction of the diatoms similar extraction method asphytoliths was followed (Pearsall, 2000). From each sample anaverage of 200 diatoms were counted. Diatoms and palynotaxahave been considered together for making frequency distribution.

4. Site chronology and d13c records

4.1. Chronology of the site

Earlier in their studies on late Quaternary geomorphic evolu-tion of Ziro Lake Basin from seven consecutive profiles along theNeS transect, Srivastava et al. (2009b) established the chronologyof the neotectonics that took place in this basin between 22 and

14 ka using IRSL. Two 14C dates from the studied profile are furtherinvolved in this study to shed light on the climatic events thatresulted into the shift in vegetation cover of the region in the laterphase of the Holocene. The other dates used in this study areluminescence dates around the study area, dated using coarsegrained feldspar by Srivastava et al. (2009b). These luminescencedates have been used from two nearby sections from the southernpart of the basin adjacent to present studied profile for correlatingclimatic events with the chronology of the site (Table 1). In orderto check whether the sedimentation pattern is a regional repre-sentative or not, particularly when the phenomenon is related toan intermontane lake basin such as Ziro, we have placed ourstudied section in the longitudinal geomorphic profile of Lake Ziro(Srivastava et al., 2009b) along with seven more studied sectionsby Srivastava et al. (2009b) considering the altitude andgeographical coordinates (Fig. 3). In all the cases, vertical faciesvariation and thickness are more or less similar. Fig. 3 shows the

lithological and chronological correlation of the sections.Srivastava et al. (2009b) suggested that there exists a NeS asym-metry in the basin geometry and southern part of the lake isgeomorphologically rejuvenated. Hence, luminescence dates haveonly been taken from two neighbouring southernmost sections ofthe basin to reconstruct climatic events in the Soro nala profile. Interms of lithological attributes, these sections correlate satisfac-torily. Hence, we have taken the Soro nala profile as a type sectionto represent climatic variability in the Ziro Lake Basin. The age ofstudied profile ranges between pre LGM (>19.5 ka) to latest Ho-locene (w1 ka). On the basis of IRSL ages, Srivastava et al. (2009b)suggested an age of lake formation between 14 and 10 ka. 14C agesobtained in the present study derived from near surface lacustrinedeposits are mid- to late Holocene, in stratigraphic consistencywith previously published data. As feldspars are prone to anom-alous fading, the lithological similarity between the earlier studied(by Srivastava et al., 2009b) and present profile has also beentaken into consideration.

4.2. d13C as climate indicators

Stable carbon isotopic signatures (d13C) in sediments are knownto serve as an additional proxy in long-term environment analysis.Generally, terrestrial plants are known to have two major modes ofphotosynthetic pathways, C3 and C4 cycles. C3 plants (inhabitingmoist environments) produce organic matter with d13C valuesranging between �23& and �30&, while C4 plants (growing indrier environments) produce organic matter with average d13Cvalue of w13& (Meyers, 1994). Even a minor change in humidityearidity gradient can be interpreted using d13C values of soil organicmatter considering the relative abundance of C3 and C4 plants of astudy site (Desjardins et al., 1996; Cerling, 1999; de Freitas et al.,2001; Bowman and Cook, 2002; Mora and Pratt, 2002).

Table 1Details of age data used in chronology building of Ziro lake basin, Arunachal Pradesh.

Sample no. Localityname

GPS locations/co-ordinates Profilelength (m)

Material dated Sample position inthe subsurfaceprofile (cm)

Methodused

Age (B.P) Age (ka) (1s error) Reference

Latitude Longitude

BS 2606 Ziro 27� 320 01.22 93� 490 49.2400 3.4 Clayey silt 20 14C 1370 � 71 1.29 � 0.05 Present studyBS 2607 27� 320 01.22 93� 490 49.2400 3.4 Clayey silt 60 14C 3540 � 150 3.86 � 1.60

Core no./sample no.

Localityname

GPS locations/co-ordinates Profilelength (m)

Material dated Sample position inthe subsurface profile

Method used SAR age (ka) Reference

Latitude Longitude

LD-101 Ziro lake 27� 320 01.9 93� 490 49.2400 20 Coarse grainedfeldspar

Shown in Fig. 3 IRSL 19.5 � 1.7 Srivastava et al., 2009bLD-105 27� 310 8.9 93� 500 43.500 18 Shown in Fig. 3 IRSL 10.2 � 2.7

R. Ghosh et al. / Quaternary International 325 (2014) 13e29 15


The d13C values of sediment organic matter of the entire Soronala profile (excluding the samples from coarse sand-conglomeratelayer) range between �23& and �31.24& (Fig. 4, SupplementaryTable S1). The data imply overall dominance of C3 plants in thevegetation of the region since pre-LGM time with a general coolehumid environment. However, to estimate the relative contributionof C3 and C4 plants in the regional vegetation, a mass balancecalculation (Thornton and McManus, 1994) has been applied usingthe sediment d13C values. The fractional contribution of C3 organicmatter has been calculated using the following equation:

d13Cbulk ¼ fC3 � d13CC3 þ fC4 � d13CC4

where, d13Cbulk ¼ carbon isotopic ratio of the bulk, fC3 ¼ C3 fraction,fC4 ¼ C4 fraction, d13CC3 (�28&) and d13CC4 (�13&) are the averagevalues for C3 and C4 plants respectively (Meyers, 1994). The esti-mations show that between 340 and 60 cm depths i.e. during pre-

LGM to 3.8 ka the areawas exclusively C3 dominated (the values forcoarse sand-conglomerate sequence that signifies the LGM span areunknown). However, during 3.8e1.2 ka onwards a gradual increasein C4 plants resulted in an alteration of the C3eC4 abundance of theregion, where C3:C4 ratio changed from 76:24 to 66:34 (Fig. 4). Theprofile shows a steady enrichment in d13C values from �24.5&to �23& (w1.5%) 3.8 ka onwards, while during pre-LGM time to3.8 ka, d13C data indicates a large depletion from �28.2&to �31.24& (>3&).

5. Phytolith and pollen records

5.1. Phytoliths: application of indices vs. general approach

Phytoliths, the tiny opaline siliceous structures of plant origin,have been used to reconstruct the late Quaternary palaeoclimateand palaeoenvironments in a variety of sediments, including loess

Fig. 1. Location of sample collection, in Ziro Lake Basin, Arunachal Pradesh, Eastern Himalaya.



(Lu et al., 1996; Madella, 1997; Blinnkov et al., 2002); lake mud(Carter, 2002); sand dunes (Horrocks et al., 2000); tephra sections(Sase et al., 1987), coastal plain sequences and other sediments(Fredlund and Tieszen, 1997; Pearsall, 2000; Lu et al., 2002;Abrantes, 2003; Piperno and Jones, 2003). After the decay ofplant tissues, they remain within the sediment as dispersedmicrofossils.

Grass short cell phytoliths (GSCP) help in identifying up to tribelevel and offer a much more detailed reconstruction of grasslandcover. The distinctive shapes of these tiny particles allow fordiscrimination between forest and grassland vegetation, grasslandsthat are C3 Pooideae (cool wet), C4 Panicoideae (warm humid) andC4 Chloridoideae (warm dry) (Twiss, 1987; Fredlund and Tieszen,1994, 1997; Alexandre et al., 1997; Barboni et al., 1999). Due tothe short life cycle and rapid adaptability to changing environ-ments, grasses respond very sharply to climatic oscillations. Changein temperature, rainfall, and CO2/O2 concentration can alter thecomposition of C3 and C4 elements in any grass cover (Ficken et al.,2002).

Two basic approaches in phytolith research are known i.e.analysis of assemblages that considers phytolith morphotypes ofall the recovered size category (Runge, 1996, 1999, 2000a,b, 2001;Mercader et al., 2000; Vrydaghs and Doutrelepont, 2000;Strömberg, 2004; Albert et al., 2006, 2009; Bamford et al., 2006)and the indices approach (Alexandre et al., 1997; Barboni et al.,1999, 2007; Brémond et al., 2005a, 2005b, 2008; Alexandre andBremond, 2009; Strömberg, 2009a,b), which considers only alimited numbers of well-defined morphotypes (<60 mm) toexplore the climatic parameters (temperature, degree of aridityetc.) of a site more precisely. The indices do not rely on any singlephytolith morphotype diagnostic of a particular species, genus, orfamily. Instead, they refer to the assemblages mostly recoveredfrom different subfamilies of Poaceae (Fredlund and Tieszen,1994). They help in tracing the changes in climatic patternsdepending upon the changes in composition of the grass cover ofan area.

For a comprehensive palaeoclimatic reconstruction, analysis ofphytolith assemblage was done and four phytolith indices used to

Fig. 2. Present day climate in Ziro Lake Basin, Eastern Himalaya.

Fig. 3. Longitudinal geomorphic profile of Lake Ziro showing location of the studied profile and lithology (modified after Srivastava et al., 2009b).



distinguish tree cover density (D/Po) (Brémond et al., 2008), climate(Ic%) (Twiss, 1987), humidityearidity (Iph%) (Diester-Haas et al.,1973) and water stress (Fs%) (Brémond et al., 2005b) conditionsof the area during the time of deposition. Relative ratios of differentphytolith morphotypes can be directly linked to environmentalconditions and some authors have applied phytolith ratios(referred as indices) to reconstruct changes in past climate andvegetation (Tieszen et al., 1979; Alexandre et al., 1997; Ghosh et al.,2008).

5.1.1. Tree cover density index (D/Po)The D/P index (Brémond et al., 2005a) is the ratio of ligneous

dicotyledonous morphotypes (globular granulate) against charac-teristic poaceous morphotypes. The formula for calculation of D/Phas been modified several times. Brémond et al. (2008) hasexcluded point shaped trichomes and bulliform morphotypes fromtheir D/P formula and termed them as D/Po. They considered onlygrass short cell phytoliths (GSCP) due to their potential as in-dicators up to the subfamily level. Here, the latest modified formulaby Brémond et al. (2008) has been used for calculation of tree coverdensity index.

5.1.2. Climatic index [Ic (%)]The climatic index [Ic (%)¼ Pooid/Pooidþ Chloridoidþ Panicoid]

proposed by Twiss (1987) indicates that the ratio of production ofC3/C4 phytolith morphotypes is influenced by climate and help indifferentiating coolewet from warmedry conditions. This indexrepresents the ratio of pooid versus sum of pooid, chloridoid andpanicoid types. Abundance of pooid morphotypes suggests highlatitude and altitude in the tropics (Tieszen et al., 1979; Livingstoneand Clayton, 1980; Twiss, 1992). High Ic values indicate dominanceof pooid (C3) grasses in the assemblage.

5.1.3. Humidityearidity index [Iph (%)]The humidityearidity index [Iph (%)] (Diester-Haas et al.,

1973) is used to distinguish between mesic and xeric grasslandconditions [where Iph (%) ¼ Chloridoid/Chloridoid þ Panicoid].

Earlier works in different climatic regions of the world havesuggested different value boundaries for Iph separating tall grassfrom short grass, indicators of mesic and xeric phases respec-tively. Values >40% were found to be associated with arid phasesin the northern Sahara during PleistoceneeHolocene (Diester-Haas et al., 1973), while Alexandre et al. (1997) observed that avalue of 30% separates short grass savannas in some modern andHolocene phytolith assemblages in Senegal and the Congo.However, Kurmann (1985) and Fredlund and Tieszen (1994)suggested a boundary of 45% for separating short and tallgrasses in the prairies of North America. Higher values of Iphindicate dominance of chloridoid grasses among C4 grassespresent in the assemblage, thereby suggesting xeric (warmedry)conditions. In contrast, low values of Iph suggest dominance ofmesophytic panicoid grasses that are indicators of warmehumidclimate.

5.1.4. Water stress index [Fs (%)]This index introduced by Brémond et al. (2005b) is the per-

centage of fan-shaped bulliform cell phytolith morphotypes inrelation to the sum of characteristic phytoliths. Bulliform cells arefound to occur in the epidermal regions of grasses and sedges(Andrejko and Cohen, 1984). When a leaf becomes dehydrated, theouter epidermal walls of these swollen cells contract in widthwhich results in a leaf rolling response to moisture loss (O’Tooleand Cruz, 1980; Hsiao et al., 1984; Moulia, 1994; Hernandez et al.,1999). Two factors controlling leaf rolling are high rate of transpi-ration and water stress (Brémond et al., 2005b). Silicified bulliformcells were found to develop in higher frequency when the rate oftranspiration was highest and the root system is submerged(Andrejko and Cohen, 1984).

The observed phytolith morphotypes are classified into 14different categories (Table 2). Among these 14 morphotypes, 12 arefound to occur in the members of Poaceae (bilobate, cross, shortsaddle, long saddle, circular, rectangular, rondel, trapezoids, bulli-form cell, elongated smooth, elongated sinuous and point-shaped),the globular granulate morphotypes are commonly produced in

Fig. 4. Showing a. d13C spectra of the profile b. ratios of C3 and C4 plants throughout the profile c. variation of phytolith indices along the profile.



sclerenchyma of woody dicotyledonous plants (Geis, 1973;Scurfield et al., 1974; Laroche, 1976; Welle, 1976; Bozarth, 1992),and the globular echinate morphotypes are characteristic of themembers of Arecaceae (Piperno, 1988).

The distribution of different phytolith morphotypes along theSoro nala profile is presented in Fig. 5. Four zones have beenidentified in the profile on the basis of frequency distribution ofphytolith assemblages, phytolith indices and cluster analysis (doneusing CONISS). Throughout the profile, dominance of grass phyto-lith morphotypes was observed over non-grass types. As grassesare dominant and more diverse phytolith producers than arearboreal plants, underrepresentation of woody dicot morphotypesin the assemblage is understandable.

5.1.5. Zone I (>19.5 ka, 340e290 cm)Depths between 340 and 310 cm of this zone is composed of

alternating fine sand and silt, and sediment between 310 and290 cm consists of sand and conglomerate. Conglomerates wereexcluded from the samples during phytolith extraction. Among thenon-grass morphotypes, globular granulates (78e95%) dominateover globular echinate morphotypes (5e24%). Among the GSCPmorphotypes, prevalence of pooid morphotypes (w8e16%) wasnoted, followed by panicoid (w6e11%), and chloridoid morpho-types (w1.5e11%). Bambusoid long saddles were retrieved in sig-nificant frequencies (w3e7%). Of the grass elongatedmorphotypes,bulliform cell morphotypes have also been recovered in significantpercentages (w2.3e5.8%), while point-shaped, elongated sinuousand elongated smooth end morphotypes have been recovered innegligible, inconsistent frequencies (Fig. 5).

Of the phytolith indices, D/Po ranges between w1 and 1.5, Icvaries between w30 and 68.5%, Iph fluctuates between 21 and 60%and Fs between w8.5 and 18%. In this zone, most of the studiedsamples except that at 290 cm depth have shown Ic values >30%(mean 51.85%), whereas most of the Iph values were <30% (mean33.5%). Values of d13C range between �30& and �31.24& (Fig. 4).

5.1.6. Zone II (>19.5e10.2 ka, 290e150 cm)This zone is mainly composed of coarse sand and conglomerate.

An abundance of pooid morphotypes (w8e14%) was noticed in theGSCP assemblage, although the frequency of chloridoid morpho-types (w8e16%) and panicoids (w8e10%) increased. A noticeabledecrease occurred in bambusoid long saddles (w1.6e3%). Fre-quency of silicified bulliform cells (w4e7%) increased slightly overzone I. Among the non-grass types, dominance of globular

granulate morphotypes (83e95%) over the globular echinate mor-photypes (5e17%) is evident in this zone (Fig. 5).

A significant decline in values of D/Po (w0.6e1) has beennoticed compared to those of zone I. Samples between depths 250e

190 cm show D/Po values ranging between w0.6 and 0.8. Adecreasing trend in Ic values (w22e44%) and corresponding in-crease in Iph values (w51e72%) characterized this zone. Increase inFs values (w12e20%) may be due to corresponding increase ofproduction of bulliform cells by grasses in response to increase inaridity during the time of deposition. As this part of the profile iscompletely composed of coarse sand and conglomerate, no stablecarbon isotopic analysis was done (Fig. 4).

5.1.7. Zone III (10.2e3.8 ka, 150e60 cm)This zone is represented by blackish carbonaceous clayey silt. An

increment in globular echinate morphotypes (w12e20%) thanthose in the earlier zone was observed. Globular granulates areprevalent in the arboreal phytolith assemblage (w83e88%). Amongthe GSCP morphotypes, a prevalence of pooids (w8e16%) has beennoticed in the assemblage and their frequency of occurrenceincreased over zone II. On the other hand, the frequency of panicoid(w7e9%) and chloridoid morphotypes (w2.5e4%) declined fromzone II. Bambusoid saddle’s frequency (w2e7%) increased. Of theelongated morphotypes, the percentage of bulliform cells variesbetween w2.5 and 5%, slightly lower than that in zone II (Fig. 5).

Of the phytolith indices, a considerable rise in values of D/Po

(w1.1e2) occurs, in comparison to that of zone II. Values of Ic(w41e61%) have also been amplified considerably over zone II. Incontrast, values of Iph (w22.6e35%) and Fs (w11e16%) declinedsignificantly. Stable carbon isotopic values range between �29.1&and �28.2& (Fig. 4).

5.1.8. Zone IV (3.8 ka onwards, 60e10 cm)This zone comprises blackish carbonaceous clayey silt. Globular

echinate morphotypes are absent in this zone. Among the GSCP, asubstantial increase in both chloridoid (w5e10%) and panicoid(w8e13%) morphotypes in comparison to that in zone III wasnoted. However, both pooid morphotypes (w11e12%) and bam-busoid morphotypes (w2e5%) decreased a little from zone III. Thefrequency of bulliform morphotypes (w4.5e7%) increased (Fig. 5).

Among the phytolith indices, D/Po ranges between w0.8 and 1,showing a decreasing trend compared with zone III. A significantdecline in Ic values (w33e48%) compared to zone III is also note-worthy. Values of Iph (w39e47%) also show a considerable rise incomparison to zone III, while Fs (w11e16%) values are similar to

Table 2Phytolith morphotypes identified in Soro nala profile with their taxonomic attributes.

Morphotypes Taxonomic attribution References

Globular granulate cf. Dicotyledonous Bozarth, 1992; Geis, 1973; Laroche, 1976; Scurfield et al., 1974; Welle, 1976Globular echinate Arecaceae Piperno, 1988; Runge, 1999Bilobate Poaceae, Panicoideae Twiss et al., 1969; Brown, 1984; Mulholland, 1989; Fredlund and Tieszen, 1994; Lu and Liu, 2003Cross Poaceae, Panicoideae Twiss et al., 1969; Brown, 1984; Mulholland, 1989; Fredlund and Tieszen, 1994; Lu and Liu, 2003Short saddle Poaceae, Chloridoideae Prat, 1936; Twiss et al., 1969Long saddle Poaceae, Bambusoideae Tieszen et al., 1979; Livingstone and Clayton, 1980Circular Poaceae, Pooideae Twiss et al., 1969; Pearsall, 2000Rectangular Poaceae, Pooideae Twiss et al., 1969; Pearsall, 2000Rondels Poaceae, Pooideae Twiss et al., 1969; Pearsall, 2000Trapezoids Poaceae, Pooideae Twiss et al., 1969; Pearsall, 2000Bulliform cells (cuneiform

and parallelepipedal)Poaceae Twiss et al., 1969; Twiss, 1992

Elongated smooth Poaceae Twiss et al., 1969Elongated sinuous Poaceae Twiss et al., 1969Point-shaped Poaceae Bozarth, 1992; Pearsall, 2000



those in zone III. Stable carbon isotopic values rangebetween �23& and �24.1& (Fig. 4).

Relative contributions of C3/C4 plants in the regional vegetationhave been estimated using a simple mass balance calculation(Thornton and McManus, 1994). Between 340 and 60 cm depths ofthe profile, the chief contribution was from C3 plants (as valuesranging between �28.2& and �31.24&). In zone IV (betweendepths 60e10 cm), a significant increase of C4 plants resulted in adecline in C3:C4 ratio from 76:24 to 66: 34 (Fig. 4).

5.2. Canonical correspondence analysis and phytolith assemblage

To test the reliability of phytolith assemblages and phytolithindices in palaeoenvironmental reconstruction, Canonical Corre-spondence Analysis (CCA) has been performed using CANOCO 4.5for Windows on the complete phytolith data set. CCA is a multi-variate analysis that explains the relationships between biologicalassemblages of species and their environment (ter Braak, 1986,1987; ter Braak and Verdonschot, 1995). A constrained ordinationof species data in response to climate variables has been performedby this method. CCA has been used here to reveal the climatic pa-rameters (as reflected by phytolith indices including tree coverdensity index, climatic index, humidityearidity index and waterstress index) that best reflect the main patterns of variation in thefossil phytolith data.

The first two axes explain 29.2% and 12.4% of the total variationin the phytolith dataset. The amount of variations explained by theaxes as a fraction of total explainable variations is represented bythe cumulative percentage variance of specieseenvironment rela-tion. The two axes taken together display 79.9% of the variationsthat can be explained by the variables.

The eigenvalues of axis 1 and axis 2 are 0.05 and 0.02 respec-tively. The specieseenvironment correlations indicate howmuch ofthe variation in the phytolith data on one CCA axis is explained bythe environmental variables. CCA axis 1 accounts for 56.1% of thespecieseenvironment relation. The value 0.90 suggests that theclimatic variables can account for most of the variation in thephytolith data on CCA axis 1. In Fig. 6, the lengths and positions ofthe arrows depend on the eigenvalues and provide informationabout the relationship between the climatic variables and thederived axes (Jongman et al., 1987). Arrows parallel to an axisindicate a correlation. The length of the arrow reflects the strengthof that correlation. Climatic variables with long arrows are morestrongly correlated with the ordination axes than those with shortarrows. Thus, Iph is strongly related to axis 1 and least to axis 2,whereas Ic is inversely related to Iph, showing a strong relation toaxis 2. D/Po and Fs are inversely related to each other. However,they are not highly related to either axis 1 or axis 2. Short saddle,bilobate and cross-shaped morphotypes, indicators of warmedryconditions are located on one end and trapezoid, circular, rondeland rectangular morphotypes which are indicators of coolemoistclimatic are located on the other end of axis 1, whereas globulargranulate, long saddle lie on the other end of axis 2. Samplenumbers (Ziro-1eZiro-5) and (Ziro-16eZiro-21) show a close as-sociation with axis 1 and Iph index. Sample numbers (Ziro-6eZiro-15 and Ziro-22eZiro-26) indicate a strong relation with D/Po and Icindices.

5.3. Palynoassemblage analysis

Palynological investigations of sediments have shown fair timecorrespondence among vegetation and climate reconstructions

Fig. 5. Phytolith spectra in Soro nala profile, Arunachal Pradesh.



through ages. A total of 64 palynotaxa (both pollen and non-pollenpalynomorphs) were identified in the Soro nala profile. Samplesbetween depths 170e310 cm did not yield any palynotaxa. Asummary of the percentage of the palynomorphs has been repre-sented in the pollen diagram (Fig. 7). Among the identified pollentaxa, Abies, Larix, Podocarpus, and Juglans are presently not com-ponents of the local vegetation cover in and around the Ziro LakeBasin. These taxa are found in the comparatively higher elevationzones and are elements of temperate broad leaved and coniferousforests of nearby elevated regions of Upper Subansiri, Lower Sub-ansiri, and Kameng districts. Among the non-pollen palynomorphs,four algal species and seven pteridophytic members have beenrecovered. Cluster analysis was done on the frequency data ofpalynomorphs using CONISS, and three zones have been identified.

5.3.1. Zone I (>19.5 ka, 340e320 cm)This zone is characterized by the dominance of arboreal plants

(AP) (72e75%) over hygrophilous elements (12e16%) and non-arboreals (12e14%). The pollen record identifies the regionalpresence of Pinus, Alnus, Aralia, Arecaceae, Anacardiaceae, Betula,Quercus, Schima, and Symplocos and some other taxa representing amixed sub-tropical broad leaved-pine forest. Some temperate treepollen including Abies, Juglans, and Ulmus have also been retrievedin small frequencies. Although in general most pollen grains aretransported upslope, small quantities of pollen grains are known tobe transported downslope (Fall, 1992).

Hygrophilous elements are represented by moisture lovingpteridophytes including Cyathea and Lycopodium (although innegligible percentages) as well as by the diatoms Navicula, Eunotiaand Amphora. Anothermember, Concentricystes (Christopher,1976),also known in the literature as Pseudoschizaea (Scott, 1992), isincluded here because it is likely to be of algal origin (Milanesi et al.,2006). Prevalence of freshwater diatoms and Concentricystes in theassemblage of hygrophilous members is suggestive of the presenceof a stream in the vicinity of the area. Non-arboreal taxa are rep-resented by very small percentages of Asteraceae, Capparidaceae,Caryophyllaceae, Cucurbitaceae, Gesneriaceae Liliaceae, Malvaceae,Menispermaceaea, Polygonaceae, and Poaceae.

5.3.2. Zone II (10.2e3.8 ka, 150e60 cm)A significant increase (10e31%) in hygrophilous elements was

noted, particularly the marsh inhabiting taxa Lycopodium, Mar-attiaceae, Osmunda, Polypodiaceae, Pteris, Thelypteris, Cyperaceae,and Typha. However, the frequency of diatoms and Concentricystesdeclinedmore than in zone I indicating that the stream receded to amarginal swamp, as illustrated by the abrupt expansion of marsh-inhabiting taxa. A considerable reduction of non-arboreals (5e19%) and corresponding increase of arboreals (55e84%) is sugges-tive of a more dense forest cover around the site. Downslopetransport of Abies, Larix, Podocarpus, Juglans and Ulmus has alsobeen observed here.

5.3.3. Zone III (3.8 kaesub-recent, 60e10 cm)A considerable increase in NAP (43e52%) (non-arboreal plants)

characterizes this zone. Increase in heliophytic taxa like Asteraceaeand Cheno-ams as well as Poaceae indicates an increase in drynessand a thinning of forest cover. A corresponding decrease of AP (41e46%) also strengthened the assumption. Alterations have not onlytaken place in the frequency of recovery of total AP, but a significantchange has also been noticed in the assemblage. An increase in dryclimate-inhabiting taxa including members of Fabaceae andEuphorbiaceae (Punyasena et al., 2008) has been seen in theassemblage of AP in comparison to zone I and II. Arecaceae andTerminalia are absent in this zone. A reduction in frequency of

hygrophilous taxa (7e17%) from the earlier zone with a significantrise in NAP suggests a possible hydrological transformation in thearea.

5.4. Coexistence-approach and pollen-based quantitativereconstruction of temperature and precipitation

The climatic factors of mean annual temperature (MAT) andmean annual precipitation (MAP) of Ziro Lake Basin during pre andpost LGM times have been obtained by applying a coexistenceapproach (CA) to 41 palynotaxa from an assemblage of 64 taxa(Table 3). Taxa with cosmopolitan distribution and those whichhave been identified up to family level have been excluded from theCA dataset. The analysis uses the nearest living relative species ofthe fossil taxa and superimposes the climatic tolerance range ofeach nearest living relative species, the overlapping of which canreflect the palaeoclimate. In general, a close relation between aplant fossil and its NLR and higher number of identified taxa leadsto a higher resolution and accuracy in climatic estimation(Mosbrugger and Utescher, 1997). Determination of varying toler-ance range for different plant taxa involves the following steps (i)confirmation of the distribution range of the plant species (Sharmaand Sanjappa, 1993, 1997; Sharma et al., 1993; Hajra et al., 1997;Sahni, 2010); (ii) using the meteorological data [http://www.cru.uea.ac.uk/data 3.1, 0.5� � 0.5� gridded versions, 1901e2009(Mitchell and Jones, 2005)] of the sites of present day distribution;(iii) defining the maximum and minimum value of the meteoro-logical data to get the plant tolerance range of the climate; and (iv)lastly, the climatic interval of each parameter of all NLRs is over-lapped and the coexistence interval of all NLRs is obtained. Theclimatic conditions under which the fossil flora once lived are bestrepresented here as the coexistence interval. A common tolerancerange of MAT and MAP for all the 41 taxa has been represented inFig. 8. Graphical representation of MAT andMAP along the profile isrepresented in Fig. 9. The CA result shows that prior to the LGM(>19.5 ka) MAT was 19.3 � 0.001 �C (all the uncertainties are �2sigma), whereas MAP was about 1925 � 15 mm (SupplementaryTable S2 and S3) in the region. Later, during 10.2e3.8 ka, MATwas found to be about 19.4 � 0.5 �C and MAP to be about1901 � 41.3 mm. Since 3.8 ka, MAT ranges between 19.7 � 0.68 �C,while MAP was between 1861 � 33.4 mm.

Table 3Palynotaxa used in CA for Soro nala profile together with their nearest living rela-tives (NLRs).

No. Palynotaxa and NLRs No. Palynotaxa and NLRs

1 Cyathea sp. 22 Dalbargia sp.2 Lycopodium japonicum 23 Desmodium sp.3 Osmunda sp. 24 Galium sp.4 Pteris sp. 25 Hydrocotyle sp.5 Thelypteris sp. 26 Ilex sp.6 Abies 27 Impatiens sp.7 Larix 28 Juglans sp.8 Pinus 29 Magnolia sp.9 Podocarpus sp. 30 Polygonum sp.10 Alnus sp. 31 Quercus sp.11 Allium sp. 32 Rumex sp.12 Aralia sp. 33 Schima sp.13 Artemisia sp. 34 Sida sp.14 Bauhinia sp. 35 Sterculia sp.15 Berberis sp. 36 Symplocos sp.16 Betula sp. 37 Terminalia17 Calamus sp. 38 Triumfetta sp.18 Cassia sp. 39 Typha sp.19 Cerastium sp. 40 Ulmus sp.20 Clerodendron sp. 41 Viola sp.21 Cuscuta sp.



5.5. Canonical correspondence analysis and palynoassemblages

Canonical correspondence analysis was performed on the fre-quency dataset of palynomorphs, taking the MAT and MAP derivedthrough CA analysis values as climatic variables. The analysis wasperformed to explore the correlation between plant species andclimatic parameters. The first two axes explain 25.4% and 14.7% ofthe total variation in the palynomorph dataset. The eigenvalues ofaxis 1 and axis 2 are 0.1 and 0.04 respectively. CCA axis 1 accountsfor 68.3% of the specieseenvironment relation. In Fig. 10, climaticvariables i.e. MAT is strongly related to axis 1 and least related toaxis 2, while MAP is inversely related to MAT. Dry climate indicatortaxa i.e. Asteraceae, Cheno-ams, Euphorbiaceae, Fabaceae, andPoaceae are located on one end, and wet loving tree members suchas Alnus, Betula, Quercus, Schima, and Facourtiaceae are located onthe other end of axis 1.

6. Discussion

Among several other factors, climate controls plant distributionand existence of a particular species in an environment, implyingthat the plant’s growth can adapt to particular climatic conditions(Good, 1974; Gribbin, 1978). Vegetation develops only when theclimate is suitable for each plant taxon in a community (Wang,1992). We have tried to explore the planteclimate interaction inZiro Lake Basin across the LGM time using pollen, non-pollenpalynomorphs, and stable carbon isotopic spectra.

Using the proxy records as well as results of CCA and CA ana-lyses, four distinct climatic phases were observed in the Ziro LakeBasin. Srivastava et al. (2009b) studied the evolution of Ziro LakeBasin and investigated the geomorphic changes of this area duringthe late Quaternary (w22e10 ka). Here, we focus on the vegetationresponse to the climate and geomorphic changes since pre-LGM(>19.5 ka) to recent. Accompanying changes in the hydrologicalcycle are also discussed in this context.

6.1. A humid climatic phase with a dense closed semi-evergreenforest before the LGM

A dense semi-evergreen- broad leaved closed forest mixedwith conifers was prevalent in the area during this time, asobserved by the higher percentages of arboreal pollen grains ofPinus, Alnus, Quercus, Araliaceae, Arecaceae, Berberidaceae, Erica-ceae, Fabaceae, and Meliaceae. Occurrence of non-arboreals inlower frequency also strengthens this argument. Moderate re-covery of extra local elements including Abies, Juglans, and Ulmusthat are now growing in the nearby comparatively higher eleva-tion zones of temperate broad leaved and coniferous forest ofUpper Subansiri, Lower Subansiri and Kameng districts indicatesthat they were carried to the site by downslope winds. Variationsin hygrophilous taxa along the Soro nala profile reflect a possiblehydrological transformation. Occurrence of lotic environment-inhabiting algal taxa and pteridophytes suggests a water source,possibly a stream during pre-LGM time. The geomorphic study of

Fig. 6. Triplot of CCA on phytolith data of the Soro nala samples: ordination diagram with climatic variables (phytolith indices) represented by arrows, phytolith morphotypes bydark dots and samples by dark squares.



Srivastava et al. (2009b) in the area reveals that Kale River (Fig. 2)with limited catchment presently drains the lake basin and beforew21 ka, the valley was drained by a high energy palaeochannel.Presence of a 150 cm long sequence of coarse sand andconglomerate in the profile is in conformity with the above fact.CA data indicates that prior to the LGM, MAT (w19.3 �C) was alittle higher (w0.8 C�) than that of present day (w18.5) in ZiroLake Basin, whereas MAP was w1925 mm, about 94 mm (onaverage) higher than the present day value (1831 mm).

The phytolith record suggests dominance of woody dicots overArecaceae, indicating a dense closed forest with palms. Prevalenceof pooid morphotypes in the grass phytolith assemblage is sug-gestive of a moist environment. However, moderate recovery ofpanicoid morphotypes adapted to warmehumid climatic conditionreveals that the overall climate was moist-subtropical. Generally,chloridoid grasses are adapted towarm and dry climatic conditions.Hence their recovery in negligible frequency also suggests a humid-subtropical climatic condition during this phase. Generally, silici-fied bulliform cells develop in higher frequencies when the rate oftranspiration is higher. Upon dehydration of leaves, the outerepidermal walls of these cells acquire the ability to contract inwidth, promoting the grass leaf-rolling response to moisture loss(O’Toole and Cruz, 1980; Hsiao et al., 1984; Moulia, 1994;Hernandez et al., 1999). The two factors controlling leaf-rollingare high transpiration rate and water stress. Hence, occurrence ofbulliform cells in low frequency during this phase is suggestive oflower rates of transpiration by plants, in turn indicating a wet cli-matic condition. Stable carbon isotopic signatures of SOM (sedi-ment organic matter) support the fact that the area during thisphase was dominated by C3 plants, requiring high soil moistureavailability thereby indicating a humid climate. D/Po index, havingvalues mostly greater than unity is indicative of a semi-evergreentype of forest rather than grassland. High values of D/Po are al-ways>1 for semi-evergreen forest, whereas values<1 characterizea savanna type vegetation cover (Alexandre et al., 1997). Values of Icindex are >52% (average) which is suggestive of dominance of C3pooid grasses in the assemblage, which in turn indicates a wetclimate. Lower values of Iph, the humidityearidity index (w33.5%)are indicative of dominance of C4 panicoid grasses over C4 chlor-idoid taxa, pointing towards the existence of a mesic condition.Both C3 pooid and C4 panicoid grasses require high available soilmoisture. Co-dominance of both the (C3 and C4 moisture loving)grasses in the assemblages surmises that both summer and winterprecipitation was high during this phase which resulted in a highMAP (mean annual precipitation). High MAP, prior to the LGM, inthis lake basin might be the reason for high soil moisture whichsupported the more mesic grasses like Pooideae and Panicoideae.High values of D/Po suggesting a dense semi-evergreen forest arealso compatible, as only high precipitation and available soilmoisture can help sustain such a forest type. From the stable iso-topic data, there is an inverse relation between Ic and d13C whererise in Ic values show decrease in d13C values, as expansion of C3plants results in depletion of d13C. Dominance of C3 plants asrevealed by d13C data also suggests higher precipitation during thisphase.

6.2. Weakening of SWM and a rise in C4 grasses during the LGM

This climatic phase and corresponding vegetation response hasbeen revealed only by the phytolith data covering a time span fromthe LGM to post LGM period (w19.5 to 10.2 ka). Coarse sand andconglomerate deposits of this phase indicate the presence of a highenergy palaeochannel which used to carry coarse sand as bed load.Due to the sandy nature of the deposit, palynological and stablecarbon isotopic analyses could not be done from this part of the

Fig.

7.Pa

lyno

morph

spectrain

Sorona

laprofi

le,A

runa

chal

Prad

esh.



Fig. 8. Coexistence intervals of palynoflora for MAT (mean annual temperature) and MAP (mean annual precipitation).

Fig. 9. Changes in MAT and MAP derived through coexistence approach along Soro nala profile, Ziro basin, Arunachal Pradesh.



profile. Non-grass woody morphotypes decreased significantly, asreflected by a decline in D/Po index to<1. An increase in Iph (w60%)with respect to Ic (w32%) values indicates more expansion of C4grasses compared to C3 grasses, and an increase in aridity. Fs (%)values have also shown an increment from w12.5 to 20% in thisphase suggesting an increase in the rate of transpiration of plants.An increase in transpiration rate might be a reflection of increase indryness. The available high resolution marine and terrestrial pale-omonsoon records (speleothems and pollen records) of the Southwest monsoon (SWM) from important climatic regimes such asWestern Arabian Sea, Eastern Arabian Sea, and the Bay of Bengalsuggest that there was a considerable weakening of SWM duringthe LGM (Tiwari et al., 2011). However, there exists a considerablespatial variability in monsoon records across the different climaticzones of India, which is more pronounced on shorter timescales. Inthe Ziro Lake Basin, earlier records (Srivastava and Misra, 2008;Srivastava et al., 2008, 2009b) suggest that during the arid LGM, areduction in rainfall led to a decline in forest cover and increasedsediment production in the catchment area. Consequently, therivers might have aggraded their valleys due to increased sedimentload and decreased hydraulic energy. Phytolith evidence indicatesthat not only was the forest cover altered (as D/Po always remains<1) during the LGM, but dry loving C4 grasses also showed aconsiderable expansion during the said time might be due to aregional drop in precipitation. However, C3 grass morphotypeshave also been observed in this phase, although in reduced fre-quency. A stronger winter precipitation was evident during theLGM despite the weakening of summer precipitation (Sarkar et al.,1990). This enhanced winter precipitation might have supported

sustenance of C3 grasses during this phase. Presence of coarsesands in the deposit also supports the theory of valley aggradation.Post-LGM phytolith records suggest a gradual climatic ameliorationand restoration in forest cover as shown by an increase in D/Po

value to >1 and Ic value to >35%. From the phytolith data, duringthe LGM, a decline in regional summer precipitation was respon-sible for both alteration in forest cover and expansion of C4 grassesover C3 grasses. With the gradual improvement in post-LGM pre-cipitation regime, restoration of forest cover of the region started,and a slight increase of C3 grasses was noticed.

6.3. Post-LGM intensification of summer monsoon

This phase corresponds to a time span covering 10.2e3.8 ka. Theonset of climate amelioration has been revealed in this phase by ahigher recovery of moisture loving arboreal palynotaxa includingMeliaceae Quercus, Sterculia, Terminalia and Magnolia. NAP hasbeen recovered in reduced frequency. However, a remarkable in-crease in hygrophilous elements including the marsh inhabitingferns Osmunda, Polypodiaceae, Pteris and Marattiaceae, along withCyperaceae and Typha, has been noticed in this zone. An expansionof marsh inhabitants is suggestive of a hydrological transformationfrom a stream to a shallow lake. Lacustrine sediments seen in thestudied section strengthened the proposition of Srivastava et al.(2009b) that a hydrological transformation from a stream to lakein Ziro occurred during w14 to 10 ka. Phytolith records conformwith palynological data showing an increase in D/Po values to >1along with further corresponding increase in Ic values to >41%(average) and a decrease in Iph to <30%. Increase in both Ic and

Fig. 10. Biplot of CCA on palynological data on Soro nala samples: ordination diagram with climatic variables represented by arrows and pollen taxa by dark dots.



D/Po and decline in Iph is might be due to restored monsoonalprecipitation. During this phase MAT was derived to be 19.4 �C(average) and MAP was derived to be 1901 mm (average) throughCA analysis, signifying that the ameliorated climate helped in sus-taining a luxuriant forest cover in the area. Stable carbon isotopicdata (varying between �28& and �30&) demonstrates thedominance of C3 plants in the vegetation, indicating a humid cli-matic condition. Studies on Holocene climate from different regionsof India (Naidu, 1999) indicate a phase of intensification of summermonsoon from 12 ka onwards with highest intensification betweenw9 and w6 ka. The present study also reveals intensification ofSWM 10.2 ka onwards, which perhaps continued to 3.8 ka, indi-cating a climatic evolution from a dry phase during the LGM to apost-LGMhumid phasewith enhanced summer precipitation in theZiro Lake Basin.

6.4. A less humid climate with a shift from dense closed semi-evergreen forest to less dense mixed deciduous broadleaved-pineforest

In this phase (3.8 ka onwards), climatic alteration is moreprominent and is reflected in the vegetation cover of the area.Arboreal elements decreased significantly with correspondingincrease in non-arboreals indicating a significant thinning of theforest cover. Among the arboreals, dry climate loving taxaincluding Fabaceae and Euphorbiaceae showed prominence,along with the other broad-leaved taxa Alnus, Betula, Quercus andMagnolia in the AP assemblage, with Pinus as the only conifermember. The complete absence of Arecaceae and Terminalia,which are still absent in the present day vegetation cover of thearea, also points towards a probable change in the moistureregime. As these taxa are adapted to high precipitation zones,their absence during this phase signifies a shift in the vegetationcover of the area from a semi evergreen forest to a mixed broad-leaved deciduous-pine forest. The forest became open, as shownby the considerable expansion of non-arboreals compared toarboreal taxa. Climate of this phase became drier, and the abun-dance of Poaceae, Asteraceae and Cheno-ams in the NAP assem-blage may be due to this drier climate. A considerable decrease indiatoms and an increase in marsh inhabiting ferns indicates ashallower lake, i.e. lentic condition. Together, from phytolith andstable carbon isotopic signatures, C3 plants were still dominatingthe region. However, C4 taxa (both C4 grasses and other non-arboreal C4 taxa) have shown a significant rise in frequencyfrom earlier phases (prior to 3.8 ka) which might be an adaptationto increasing dryness. CA data also shows a slight increase in MATto 19.7 �C (average) and a drop in MAP values to 1861 mm(average). A change in stable carbon isotopic ratio and increase ingrass towards the top of the profile might indicate some humaninduced landscape change.

Vegetation response, in terms of shift from a closed semi-evergreen forest to a less dense mixed deciduous broadleaved-pine forest as a result of climatic variability across the LGM ina sub-tropical intermontane lake basin has given rise to a num-ber of questions. Whether these changes are regional or local? Doplants of comparatively lower elevation sites show climatesensitivity as do those of higher altitudes and successfully reflectsignatures of climate variability? Which of the climatic drivershas influenced plant communities more? Expansion of C4 grassesand corresponding weakening of SWM during the LGM areevident in a number of palaeoclimatic reconstructions frompeninsular India (Bhattacharyya et al., 2006 and referencestherein). A study by Sharma and Chauhan (1994) from an EasternHimalayan lake at Darjeeling at an elevation of about 1700 ma.s.l. has shown expansion of grassland and shrinkage in forest

elements during the LGM, suggesting the influence of an aridclimate. This further supports that the vegetation change andweakening of SWM during the LGM is possibly a regional phe-nomenon throughout the Indian subcontinent. Naidu andMalmgren (1996) and Naidu (1996), in their studies based onplanktonic foraminifera in Arabian Sea observed that SWMstarted ameliorating since 12 ka and reached its maximum be-tween 10 and 6 ka. Weakening of SWM began from 5 ka onwardsand is most pronounced between 3.5 and 1.2 ka. d13C stratig-raphy in the Ganges deltaic plain showed a C3 domination duringthe earliest Holocene followed by a C4 expansion during the post5 ka period (Sarkar et al., 2009). d13C stratigraphy in the Nilgiripeat bogs in southern India also suggests a preponderance ofgrassland during the LGM, followed by C3 expansion in earliestHolocene, to a second phase of C4 expansion in the latest Ho-locene (Rajagopalan et al., 1997). In Chilka lake, Indian east coast,a similar temporal change in vegetation has also been observedduring the Holocene (Khandelwal et al., 2008). During climaticreconstruction of Mirik Lake, Eastern Himalaya, Sharma andChauhan (1994) have also noticed a decline in broad-leavedforest elements and a corresponding increase in Poaceae andother dry climate loving taxa since 2 ka which suggested a slightdeterioration in climate. However, they have attributed thischange to human activities. Bera and Basumatary (2013) in LowerSubansiri Basin, north-east India also shed light on a phase ofweakening of SWM since 4200 BP. Loss of precipitation due toweakening of SWM might be responsible for this vegetationalteration in Ziro Lake Basin during the LGM. Following the LGM,SWM started intensifying, resulting in an increase in MAP, lesserthan the pre-LGM phase but sufficient for forest coverrestoration.

A spatial trend of dryness was noticed during 4.2e3.8 ka in mostof tropical Africa (Gasse, 2000, 2001) and monsoonal Pakistan. Ourstudy also indicates that a further weakening of summer monsoon3.8 ka onwards resulted in an alteration of the vegetation cover inthe Ziro Lake Basin, with further decrease in MAP. The decline ofSWM since 3.5 ka may be interpreted as being a result of the onsetof arid climate, in general throughout the tropics and in particularin the Asian tropics. As a consequence of this climatic deterioration,the vegetation has also been altered. No report was available fromsuch a low altitude sub-tropical vegetation belt of the EasternHimalayas showing signatures of monsoonal variability since thelast glaciation. This study aims to fill this gap and adds substantialinformation to explain how these change influenced the ecosystemof the region.

7. Conclusion

Multiproxy study of Soro nala profile of Ziro Lake Basin, Aru-nachal Pradesh, Eastern Himalaya provides new insights intopalaeoenvironmental and palaeoclimatic changes in the area sincepre-LGM time. Four climatic phases have been observed:

- a wet-subtropical climatic phase supporting a dense semi-evergreen forest in the area during >19.5 ka. A high energypalaeochannel in the area, as shown by an earlier study bySrivastava et al. (2009b), has also been established throughpresent palynological study.

- a drier climate duringw19.5 kamight be aweak influence of theLGM alongwith an expansion of C4 grasses in the area. However,the signature of the LGM is lacking in low altitude regions in theHimalayas. On the basis of occurrence of a similar trend in globalrecords as well as in different parts of the Indian sub-continent,a possibility of regionalism of this climatic phase cannot beruled out.



- post-LGM climate became improved due to intensification ofsummer monsoon until 3.8 ka which helped in restoration offorest cover in the area.

- the last phase revealed a shift from a dense semi-evergreenclosed forest to a less dense mixed deciduous broadleaved-pine forest under slightly warmer and drier climate.

The climate dynamics since >19.5 ka to recent also correspondsto a hydrological transformation in the area from a channel to ashallow lake.

The CCA data have also contributed significantly to enrich ourknowledge on how the plants relate to environmental signals. Bothpollen and non-pollen palynomorph data from Soro nala profileshow that MAP has played more significant role in species distri-bution than MAT in the Ziro Lake Basin across the LGM. Hence, thephytolith indices Ic (climatic index) and Iph (humidityearidity in-dex) show close relations to MAP, but not with MAT. Moistureloving taxa also have shown a similar trend.

The CA analysis reveals that since pre-LGM time, very littlechange in MAT (w1.2 C�) has been evident in Ziro Lake Basin,whereas during pre and post LGM times, MAP was higher than it istoday, by w94 mm and w70 mm respectively. However, during3.8e1.2 ka, MAP was only a little higher (w30 mm) than it is today,showing a tendency of gradual decline suggesting a progressiveincrease in dryness. Gradual recession of MAP since >19.5 ka andcorresponding vegetation shifts in the Ziro Lake Basin imply thatprecipitation is the primary influence in vegetation restructuring inthis region, along with other geomorphic changes.

Acknowledgments

The author RG thankfully acknowledges the Director, BirbalSahni Institute of Palaeobotany, Lucknow for his encouragementand permission to publish this work. The authors MAK and SBwould also like to acknowledge Mr. Shambhu Chakraborty,Geological Survey of India (GSI), Arunachal Pradesh for his helpduring the collection of samples and DST (ESS), New Delhi, forfinancial assistance.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.quaint.2014.01.046.

References

Abrantes, F., 2003. A 340,000 year continental climate record from tropical Africa-news from opal phytoliths from the equatorial Atlantic. Earth and PlanetaryScience Letters 209, 165e179.

Albert, R.M., Bamford, M.K., Cabanes, D., 2006. Taphonomy of phytoliths andmacroplants in different soils from Olduvai Gorge (Tanzania) and the applica-tion to Plio-Pleistocene palaeoanthropological samples. Quaternary Interna-tional 148, 78e94.

Albert, R.M., Bamford, M.K., Cabanes, D., 2009. Palaeoecological significance ofpalms at Olduvai Gorge, Tanzania, based on phytolith remains. Quaternary In-ternational 193, 41e48.

Alexandre, A., Bremond, L., 2009. Comment on the paper in Quaternary Interna-tional “Methodological concerns for the analysis of phytolith assemblages: doescount size matter?” (C.A.E. Strömberg). Quaternary International 193, 141e142.

Alexandre, A., Meunier, J.D., Lezine, A.M., Vincens, A., Schwartz, D., 1997. Phytolithsindicators of grasslands dynamics during the late Holocene in intertropicalAfrica. Palaeogeography, Palaeoclimatology, Palaeoecology 136, 213e219.

Andrejko, M.J., Cohen, A.D., 1984. Scanning electron microscopy of silicophytolithsfrom the okefenokee swampmarsh complex. In: Cohen, A.D., Casagrande, D.J.,Andrejko, M.J., Best, G.R. (Eds.), The Okefenokee Swamp: Its Natural History,Geology and Geochemistry. Wetland Surveys, Los Alamos, NM, pp. 468e491.

Bamford, M.K., Albert, R.M., Cabanes, D., 2006. Plio-Pleistocene macroplant fossilremains and phytoliths from Lowermost Bed II in the eastern palaeolake marginof Olduvai Gorge, Tanzania. Quaternary International 148, 95e112.

Barboni, D., Bonnefille, R., Alexandre, A., Meunier, J.D., 1999. Phytoliths as paleo-environmental indicators, West Sidi Middle Awash valley, Ethiopia. Palae-ogeography, Palaeoclimatology, Palaeoecology 152, 87e100.

Barboni, D., Brémond, L., Bonnefille, R., 2007. Comparative study of modern phy-tolith assemblages from inter-tropical Africa. Palaeogeography, Palae-oclimatology, Palaeoecology 246, 454e470.

Bera, S.K., Basumatary, S.K., 2013. Vegetation history and monsoonal fluctuationsduring the last 12,500 years BP inferred from pollen record at Lower SubansiriBasin, Assam, Northeast India. The Palaeobotanist 62, 1e10.

Bhattacharyya, A., 1989. Vegetation and climate during the last 30,000 years inLadakh. Palaeogeography, Palaeoclimatology, Palaeoecology 73, 25e38.

Bhattacharyya, A., Ranhotra, P.S., Shah, S.K., 2006. Temporal and spatial variations oflate Pleistocene-Holocene climate of the Western Himalaya based on pollenrecords and their implications to monsoon dynamics. Journal of GeologicalSociety of India 68, 507e515.

Bhattacharyya, A., Sharma, J., Shah, S.K., Chaudhury, V., 2007. Climatic changesduring last 1800 yrs BP from Paradise Lake, Sela Pass, Arunachal Pradesh,Northeast Himalaya. Current Science 93 (7), 983e987.

Blinnkov, M., Busacca, A., Whitlock, C., 2002. Reconstruction of the late Pleistocenegrassland of the Columbia basin, Washington, USA, based on phytolith recordsin loess. Palaeogeography, Palaeoclimatology, Palaeoecology 177, 77e101.

Bowman, D.M.J.S., Cook, G.D., 2002. Can stable carbon isotopes (delta C-13) in soilcarbon be used to describe the dynamics of Eucalyptus savanna-rainforestboundaries in the Australian monsoon tropics? Austral Ecology 27, 94e102.

Bozarth, S.R., 1992. Classification of opal phytoliths formed in selected dicotyledonsnative to the Great Plains. In: Rapp, G., Mulholland, S.C. (Eds.), Phytoliths Sys-tematics. Plenum Press, New York and London, pp. 193e214.

Brémond, L., Alexandre, A., Hély, C., Guiot, J., 2005a. A phytolith index as a proxy oftree cover density in tropical areas: calibration with Leaf Area Index along aforest-savanna transect in southeastern Cameroon. Global and PlanetaryChange 45, 277e293.

Brémond, L., Alexandre, A., Peyron, O., Guiot, J., 2005b. Grass water stress estimatedfrom phytoliths in West Africa. Journal of Biogeography 32, 311e327.

Brémond, L., Alexandre, A., Peyron, O., Guiot, J., 2008. Definition of grassland biomesfrom phytoliths in West Africa. Journal of Biogeography 35, 2039e2048.

Brown, D., 1984. Prospects and limits of a phytolith key for grasses in the centralUnited States. Journal of Archaeological Science 11, 345e368.

Burbank, D.W., 1983. Multiple episodes of catastrophic flooding in the PeshwarBasin during the past 700,000 years. University of Peshawar Geological Bulletin16, 43e49.

Burbank, D.W., Johnson, G.D., 1982. Intermontane basin development in the past 4Myr in the north-west Himalaya. Nature 298, 432e436.

Carter, J.A., 2002. Phytolith analysis and paleoenvironmental reconstruction fromLake Poukawa Core, Hawkes Bay, New Zealand. Global and Planetary Change 33,257e267.

Cerling, T.E., 1999. Paleorecords of C4 plants and ecosystems. In: Sage, R.F.,Monson, R.K. (Eds.), C4 Plant Biology. Academic Press, San Diego, pp. 445e469.

Chauhan, M.S., Sharma, C., 1996. Late-Holocene vegetation of Darjeeling (Jore-Pokhari), Eastern Himalaya. Paleobotanist 45, 125e129.

Christopher, R.A., 1976. Morphology and taxonomic status of PseudoschizaeaThiergart and Frantz ex R. Potonié emend. Micropaleontology 22, 145e150.

De, A., Ghosh, R., De, B., Bera, S., 2001. Palynoassemblage of Quaternary peat de-posits from Ziro Valley, Arunachal Pradesh, India. Indian Journal of Geology 73(3), 181e186.

de Freitas, H.A., Pessenda, L.C.R., Aravena, R., Gouveia, S.E.M., de Souza Ribeiro, A.,Boulet, R., 2001. Late Quaternary vegetation dynamics in the Southern AmazonBasin inferred from carbon isotopes in soil organic matter. Quaternary Research55, 39e46.

Desjardins, T., Carneiro, A., Mariotti, A., Chauvel, A., Girardin, C., 1996. Changes ofthe forest-savanna boundary in Brazilian Amazonia during the Holocenerevealed by stable isotope ratios of soil organic carbon. Oecologia 108, 749e756.

Diester-Haas, L., Schrader, H.J., Thiede, J., 1973. Sedimentological and palae-oclimatological investigations of two pelagic ooze cores off Cape Barbas, North-West Africa. ‘Meteor’ Forschungsergebnisse Reihe C 16, 19e66.

Dill, H.G., Khadka, D.R., Khanal, R., Dohrmann, R., Melcher, F., Busch, K., 2003.Infilling of the Younger KathmandueBanepa intermontane lake basin duringthe Late Quaternary (Lesser Himalaya, Nepal): a sedimentological study. JournalOf Quaternary Science 18 (1), 41e60.

Dollo, M., Samal, P.K., Sundriyal, R.C., Kumar, K., 2009. Environmentally sustainabletraditional natural resource management and conservation in Ziro Valley,Arunachal Himalaya, India. Journal of American Science 5 (5), 41e52.

Erdtman, G., 1954. An Introduction to Pollen Analysis. Waltham Mass, USA, p. 239.Fall, P.L., 1992. Spatial patterns of atmospheric pollen dispersal in the Colorado

Rocky Mountains, USA. Review of Palaeobotany and Palynology 74, 293e313.Ficken, K.J., Wooller, M.J., Swain, D.L., Street-Perrott, F.A., Eglinton, G., 2002.

Reconstruction of a subalpine grass-dominated ecosystem, Lake Rutundu,Mount Kenya: a novel multi-proxy approach. Palaeogeography, Palae-oclimatology, Palaeoecology 177, 137e149.

Fredlund, G.G., Tieszen, L.L., 1994. Modern phytolith assemblages from the NorthAmerican Great Plains. Journal of Biogeography 21, 321e335.

Fredlund, G.G., Tieszen, L.L., 1997. Calibrating grass phytolith assemblages in cli-matic terms: application to late Pleistocene assemblages from Kansas andNebraska. Palaeogeography, Palaeoclimatology, Palaeoecology 136, 199e211.

Gasse, F., 2000. Hydrological changes in the African tropics since the last glacialmaximum. Quaternary Science Reviews 19, 189e211.



Gasse, F., 2001. Hydrological changes in Africa. Science 292, 2259e2260.Geis, J.W., 1973. Biogenic silica in selected species of deciduous angiosperms. Soil

Science 116 (2), 113e119.Good, R., 1974. The Geography of the Flowering Plants, fourth ed. Longman Group

Ltd., London.Gribbin, J., 1978. Climate Change. Cambridge University Press, New York.Gupta, A.K., Anderson, D.M., 2005. Mysteries of the Indian monsoon system. Journal

Geological Society of India 65, 54e60.Ghosh, R., Gupta, S., Bera, S., Jiang, H.-E., Li, X., Li, C.S., 2008. Ovi-caprid dung as an

indicator of paleovegetation and paleoclimate in northwestern China. Quater-nary Research 70 (2), 149e157.

Hajra, P.K., Verma, D.M., Giri, G.S., 1996. Materials for the Flora of Arunachal Pra-desh. vol. I (Ranunculaceae eDipsacaceae). Botanical Survey of India, Calcutta,p. 693.

Hajra, P.K., Nair, V.J., Danie, P., 1997. Flora of India, vol. 4. Botanical Survey of India.Hernandez, M.L., Passas, H.J., Smith, L.G., 1999. Clonal analysis of epidermal

patterning during maize leaf development. Developmental Biology 216, 646e658.

Horrocks, M., Deng, Y., Ogden, J., Sutton, D.G., 2000. A reconstruction of the historyof a Holocene sand dune on Great Barrier Island, northern New Zealand, usingpollen and phytolith analyses. Journal of Biogeography 27, 1269e1277.

Hsiao, T.C., O’Toole, J.C., Yamboo, E.B., Turner, N., 1984. Influence of osmoticadjustment on leaf rolling and tissue death in rice. Plant Physiology 75, 338e341.

Iwata, S., 1987. Mode and rate of uplift of the central Nepal Himalaya. Zeitschrift furGeomorphologie 63 (Suppl.), 37e49.

Jongman, R.H.G., ter Braak, C.J.F., van Tongeren, O.F.R., 1987. Data Analysis in Com-munity and Landscape Ecology. Cambridge University Press, Cambridge, U.K.

Juyal, N., Pant, R.K., Basavaiah, N., Yadava, M.G., Saini, N.K., Singhvi, A.K., 2004.Climate and seismicity in the higher Central Himalaya during the last 20 kyr:evidences from the Garbyang Basin, Uttaranchal, India. Palaeogeography,Palaeoclimatology, Palaeoecology 213, 315e330.

Kelly, E.F., 1990. Method for Extracting Opal Phytoliths from Soil and Plant Material.Internal Report. Department of Agronomy, Colorado State University, FortCollins.

Khandelwal, A., Mohanti, M., Garcıa-Rodrıguez, F., Scharf, B.W., 2008. Vegetationhistory and sea level variations during the last 13,500 years inferred from apollen record at Chilika Lake, Orissa, India. Vegetation History and Archae-obotany 17, 335e344.

Kotlia, B.S., Bhalla, M.S., Sharma, C., Rajagopalan, G., Ramesh, R., Chauhan, M.S.,Mathur, P.D., Bhandari, S., Chacko, S.T., 1997. Palaeoclimatic conditions in theupper Pleistocene and Holocene Bhimtal-Naukuchiatal lake basin in south-central Kumaun, North India. Palaeogeography, Palaeoclimatology, Palae-oecology 130, 307e322.

Kurmann, M.H., 1985. An opal phytolith and palynomorph study of extant and fossilsoils in Kansas (USA). Palaeogeography, Palaeoclimatology, Palaeoecology 49,217e235.

Laroche, J., 1976. La silice et les plantes supericures. Revue de cytologie et de bio-logie vegetales 40, 15e45.

Livingstone, D.A., Clayton, W.D., 1980. An altitudinal cline in tropical African grassfloras and its Palaeoecological significance. Quaternary Research 13, 392e402.

Lu, H.Y., Liu, K.B., 2003. Morphological variations in lobate phytoliths from grassesin China and the southeastern USA. Diversity and Distributions 9 (1), 73e87.

Lu, H.Y., Wu, N.Q., Liu, D.S., Han, J.M., Qin, X.G., Sun, X.J., Wang, Y.J., 1996. Seasonalclimatic variation recorded by phytolith assemblages from the Baoji loesssequence in central China over the last 150,000 a. Science in China (Series D) 39,629e639.

Lu, H.Y., Liu, Z.X., Wu, N.Q., Berne, S., Saito, Y., Liu, B.Z., Wang, L., 2002. Ricedomestication and climatic change: phytolith evidence from East China. Boreas31 (4), 378e385.

Madella, M., 1997. Phytoliths from a Central Asia loess-paleosol sequence andmodern soils: their taphonomical and palaeoecologica implication. In:Pinilla, A. (Ed.), The State of the Art of Phytoliths in Plants and Soils, Mono-grafias del Centro de Ciencias Medambioentales, Madrid, pp. 49e58.

Mercader, J., Runge, F., Vrydaghs, L., Doutrelepont, H., Ewango, C.E.N., Tresseras, J.-T.,2000. Phytoliths from archaeological sites in the tropical forest of Ituri, Dem-ocratic Republic of Congo. Quaternary Research 54, 102e112.

Meetei, L.I., Pattanayak, S.K., Bhaskar, A., Pandit, M.K., Tandon, S.K., 2007. Climaticimprints in Quaternary valley fill deposits of the middle Teesta valley, SikkimHimalaya. Quaternary International 159, 32e46.

Meyers, P.A., 1994. Preservation of elemental and isotopic source identification ofsedimentary organic matter. Chemical Geology 114, 289e302.

Milanesi, C., Vignani, R., Ciampolini, F., Faleri, C., Cattani, L., Moroni, A., Arrighi, S.,Scali, M., Tiberi, P., Sensi, E., Wang, W., Cresti, M., 2006. Ultrastructure and DNAsequence analysis of single Concentricystis cells from Alta Val Tiberina Holo-cene sediment. Journal of Archaeological Science 33, 1081e1087.

Mitchell, T.D., Jones, P.D., 2005. An improved method of constructing a database ofmonthly climate observations and associated high-resolution grids. Interna-tional Journal of Climatology 25, 693e712.

Mora, G., Pratt, L.M., 2002. Carbon isotopic evidence from paleosols for mixed C3/C4vegetation in the Bogota Basin, Colombia. Quaternary Science Reviews 21, 985e995.

Mosbrugger, V., Utescher, T., 1997. The coexistence approach-a method for quanti-tative reconstructions of Tertiary terrestrial palaeoclimate data using plantfossils. Palaeogeography, Palaeoclimatology, Palaeoecology 134, 61e86.

Moulia, B., 1994. The biomechanics of leaf rolling. Biomimetics 2, 267e281.Mulholland, S.C., 1989. Phytolith shape frequencies in North Dakota grasses: a

comparison to general patterns. Journal of Archaeological Science 16, 489e511.Naidu, P.D., 1996. Onset of an arid climate at 3.5 ka in the tropics: evidence from

monsoon upwelling record. Current Science 71 (9), 715e718.Naidu, P.D., 1999. A review on Holocene climate changes in the Indian subcontinent.

Memoir Geological Society of India 42, 303e314.Naidu, P.D., Malmgren, B.A., 1996. A high-resolution record of Late Quaternary

upwelling along the Oman Margin, Arabian Sea based on planktonic forami-nifera. Paleoceanography 11 (1), 129e140.

Ning, Y.F., 2010. Methods in quantitative reconstruction of the palaeoclimate on theChinese Loess Plateau. Geological Review 56, 99e104.

O’Toole, J.C., Cruz, T.R., 1980. Response of leaf water potential, stomatal resistanceand leaf rolling to water stress. Plant Physiology 65, 428e432.

Pearsall, D.M., 2000. Paleoethnobotany: a Handbook of Procedures, second ed.Academic Press, San Diego, p. 700.

Piperno, D.R., 1988. Phytolith Analysis: an Archaeological and Geological Perspec-tive. Academic Press, New York, p. 280.

Piperno, D.R., Jones, J.G., 2003. Paleoecological and archaeological implications of aLate Pleistocene/Early Holocene record of vegetation and climate from thePacific coastal plain of Panama. Quaternary Research 59, 79e87.

Prat, H., 1936. La systematique des Graminees. Annnales des Sciences NaturellesBotanique, Series 2 (18), 165e258.

Prell, W.N., Kutzbach, J.E., 1992. Sensitivity of the Indian monsoon to forcing pa-rameters and implications for its evolution. Nature 360, 647e652.

Punyasena, S.W., Eshel, G., McElwain, J.C., 2008. The influence of climate on thespatial patterning of Neotropical plant families. Journal of Biogeography 35,117e130.

Rajagopalan, G., Sukumar, R., Ramesh, R., Pant, R.K., Rajagopalan, G., 1997. LateQuaternary vegetational and climatic changes from tropical peats in southernIndia e an extended record up to 40,000 years BP. Current Science 73 (3), 60e63.

Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., BronkRamsey, C., Buck, C.E., Burr, G.S., Edwards, R.L., Friedrich, M., Grootes, P.M.,Guilderson, T.P., Hajdas, I., Heaton, T.J., Hogg, A.G., Hughen, K.A., Kaiser, K.F.,Kromer, B., McCormac, F.G., Manning, S.W., Reimer, R.W., Richards, D.A.,Southon, J.R., Talamo, S., Turney, C.S.M., van der Plicht, J., Weyhenmeyer, C.E.,2009. Intcal09 and marine09 radiocarbon age calibration curves, 0e50,000years cal bp. Radiocarbon 51, 1111e1150.

Runge, F., 1996. Opalphytolithe in Pflanzen aus dem humiden und semi-aridenOsten Afrikas und ihre Bedeutung für die Klima- und Vegetationsgeschichte.Botanische Jahrbücher für Systematik 118, 303e363.

Runge, F., 1999. The opal phytolith inventory of soils in central Africa quantities,shapes, classification and spectra. Review of Palaeobotany and Palynology 107,23e53.

Runge, F., 2000a. Opal-Phytolithe in den Tropen Afrikas und ihre Verwendung beider Rekonstruktion paläoökologischer Umweltverhältnisse. Books on Demand,Paderborn, Germany.

Runge, F., 2000b. Les phytolithes dans les plantes, les sols et les tourbières. In:Servant, M., Servant-Vildary, S. (Eds.), Dynamique à long terme des écosystèmesforestiers intertropicaux. UNESCO, Paris, pp. 297e310.

Runge, F., 2001. Evidence for land use history by opal phytolith analysis: examplesfrom the Central African tropics (Eastern Kivu, D.R. Congo). In: Meunier, J.D.,Colin, F. (Eds.), Phytoliths: Applications in Earth Sciences and Human History.Balkema, Lisse, Netherlands, pp. 73e85.

Sahni, K.C., 2010. The Book of Indian Trees. Oxford University Press.Sanyal, P., 2007. Monsoonal rainfall variation for last 11 Ma and its impact on

vegetation study based on Indian Siwalik sediments. Himalayan Geology 28 (1),23e36.

Sarkar, A., Sengupta, S., McArthur, J.M., Ravenscroft, P., Bera, M.K., Bhusan, R.,Samanta, A., Agrawal, S., 2009. Evolution of GangeseBrahmaputra westerndelta plain: clues from sedimentology and carbon isotopes. Quaternary ScienceReviews 28, 2564e2581.

Sarkar, A., Ramesh, R., Bhattachary, S.K., Rajagopalan, G., 1990. Oxygen isotope ev-idence for a stronger winter monsoon current during the last glaciation. Nature343, 549e551.

Sase, T., Hosono, M., Utsgawa, T., Aoki, K., 1987. Opal phytolith analysis of presentand buried volcanic ash soils in Te Ngae Road tephra section, Rotorua Basin,North Island, New Zealand. Quaternary Research 27 (3), 153e163 (in Japanesewith English summary).

Scott, L., 1992. Environmental implications and origin of microscopic PseudoschizaeaThiegart and Franz ex R. Potonié emend. in sediments. Journal of Biogeography19, 349e354.

Scurfield, G., Anderson, C.A., Segnit, E.R., 1974. Silica in woody stems. AustralianJournal of Botany 22, 211e229.

Selby, M.J., 1988. Landforms and denudation of the High Himalaya of Nepal:results of continental collision. Zeitschrift fur Geomorphologie 69 (Suppl.),133e152.

Shah, S.K., Bhattacharyya, A., Chaudhary, V., 2009. Climatic influence on radialgrowth of Pinus wallichiana in Ziro Valley, Northeast Himalaya. Current Science96 (5), 697e702.

Sharma, B.D., Balakrishnan, N.P., Rao, R.R., 1993. Flora of India, vol. 1. BotanicalSurvey of India.

Sharma, B.D., Sanjappa, M., 1993. Flora of India, vol. 2. Botanical Survey of India,Calcutta.



Sharma, B.D., Sanjappa, M., 1997. Flora of India, vol. 3. Botanical Survey of India,Calcutta.

Sharma, C., Chauhan, M.S., 1994. Vegetation and climate since Last Glacial Maximain Darjeeling (Mirik Lake), Eastern Himalaya. In: Proceedings of 29th Interna-tional Geological Congress, Part B, pp. 279e288.

Sharma, C., Chauhan, M.S., 1999. Palaeoclimatic inferences from Quaternary paly-nostratigraphy of the Himalayas. In: Dash, S.K., Bahadur, J. (Eds.), The HimalayanEnvironment. New Age International, New Delhi, pp. 193e207.

Sharma, C., Chauhan, M.S., 2001. Late Holocene vegetation and climate of Kupup(Sikkim), Eastern Himalaya, India. Journal of the Palaeontological Society ofIndia 46, 51e58.

Shukla, U.K., Kotlia, B.S., Mathur, P.D., 2002. Sedimentation pattern in a trans-Himalayan Quaternary lake at Lamayura (Ladakh), India. Sedimentary Geol-ogy 148, 405e425.

Srivastava, P., Misra, D.K., 2008. Morpho-sedimentary records of active tectonics atthe Kameng river exit, NE Himalaya. Geomorphology 96, 187e198.

Srivastava, P., Misra, D.K., 2012. Optically stimulated luminescence chronology ofterrace sediments of Siang river, higher NE Himalaya: comparison of quartz andfeldspar chronometers. Journal of Geological Society of India 79, 252e258.

Srivastava, P., Bhakuni, S.S., Luirei, K., Misra, D.K., 2009a. Morpho-sedimentary re-cords from the Brahmaputra River exit, NE Himalaya: climate-tectonic interplayduring Late Pleistocene-Holocene. Journal of Quaternary Science 24, 175e188.

Srivastava, P., Misra, D.K., Agarwal, K.K., Bhakuni, S.S., Luirei, K., 2009b. Late Qua-ternary evolution of Ziro intermontane Lake basin, NE Himalaya, India. Hima-layan Geology 30 (2), 175e185.

Srivastava, P., Tripathi, J.K., Ialam, R., Jaiswal, M.K., 2008. Fashion and phases of LatePleistocene aggradation and incision in Alakananda River, western Himalaya,India. Quaternary Research 70, 68e80.

Strömberg, C.A.E., 2004. Using phytolith assemblages to reconstruct the origin andspread of grass-dominated habitats in the Great Plains during the late Eocene toearly Miocene. Palaeogeography, Palaeoclimatology, Palaeoecology 207 (3e4),239e275.

Strömberg, C.A.E., 2009a. Methodological concerns for analysis of phytolith as-semblages: does count size matter? Quaternary International 193, 124e140.

Strömberg, C.A.E., 2009b. Reply to comment on “Methodological concerns foranalysis of phytolith assemblages: does count size matter?” (A. Alexandre and L.Brémond). Quaternary International 193, 143e145.

ter Braak, C.J.F., 1986. Canonical correspondence analysis: a new eigenvector tech-nique for multivariate direct gradient analysis. Ecology 67, 1167e1179.

ter Braak, C.J.F., 1987. The analysis of vegetationeenvironment relationships bycanonical correspondence analysis. Vegetatio 69, 69e77.

ter Braak, C.J.F., Verdonschot, P.F.M., 1995. Canonical correspondence analysis andrelated multivariate methods in aquatic ecology. Aquatic Sciences 57 (3), 255e289.

Thornton, S.F., McManus, J., 1994. Application of organic carbon and nitrogen stableisotope and C/N ratios as source indicators of organic matter provenance inestuarine system: evidence from the Tay Estuary, Scotland. Estuarine, Coastaland Shelf Science 38, 219e233.

Tieszen, L.L., Senyimba, M.M., Imbamba, S.K., Troughton, J.H., 1979. The Distributionof C3 and C4 grasses and carbon isotope discrimination along an altitudinal andmoisture gradient in Kenya. Oecologia 37, 337e350.

Tiwari, M., Sing, A.K., Rengaswamy, R., 2011. High-resolution monsoon records sinceLast Glacial Maximum: a comparison of marine and terrestrial paleoarchivesfrom South Asia. Journal of Geological Research. http://dx.doi.org/10.1155/2011/765248.

Twiss, P.C., 1987. Grass-opal phytoliths as climatic indicators of the Great PlainsPleistocene. In: Johnson, W.C. (Ed.), Quaternary Environment of Kansas, Kans.Geol. Surv. Guidebook Ser., vol. 5, pp. 179e188.

Twiss, P.C., 1992. Predicted World distribution of C3 and C4 grass phytoliths. In:Rapp, G., Mulholland, S.C. (Eds.), Phytolith Systematics: Emerging Issue, Ad-vances in Archaeological and Museum Science, vol. 1, pp. 113e128.

Twiss, P.C., Suess, E., Smith, R., 1969. Morphological classification of grass phytoliths.Proceedings. Soil Science Society of America 33, 109e115.

Vrydaghs, L., Doutrelepont, H., 2000. Analyses phytolitariennes: acquis et per-spectives. In: Servant, M., Servant, V.S. (Eds.), Dynamique à long terme desecosystems forestiers intertropicaux. UNESCO, Paris, pp. 389e411.

Wang, H.S., 1992. Floristic Plant Geography. Science Press, Beijing.Welle, B.J.H., 1976. On the occurrence of the silica grains in the secondary xylem of

the Chrysobalanaceae. IAWA Bulletin 2, 19e29.Yang, S., 1996. ENSO-snow-monsoon associations and seasonal-interannual pre-

dictions. International Journal of Climatology 16, 125e134.Zhang, Q.R., 1988. Applied Regression Analysis. Geology Press, Beijing, p. 424.


Climatic variability in Ziro lake Basin

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